Effect of melt pool interference modes on mesostructure and microstructure of laser powder bed fusion fabricated Ti-6Al-4V alloy

Melt pools are critical meso-structural features inherent to the laser powder bed fusion (LPBF) process. However, there is less understanding about the interference among adjacent melt pools and its impact on the LPBF fabricated materials. This study focuses on two distinct melt pool interference modes—continuous and intermittent—and aims to investigate their influence on the local thermal profile, solidification microstructure, and mechanical properties in LPBF fabricated Ti-6Al-4V. Through a combination of numerical simulation and machine learning analysis, it is demonstrated that the thermal profile under intermittent melt pool interference is prone to heat accumulation and thermal discontinuity, leading to defects such as lack of fusion and high tensile residual stress. This interference mode also results in merging of melt pools formed in adjacent tracks, producing high cooling rates and extended thermal dwell times that coarsen the primary and secondary martensite while forming parts of lamellar and fine alpha structures. The results reveal that microstructural inhomogeneity and coarsening, along with defects generated by intermittent melt pool interference, are detrimental to the mechanical properties. In contrast, continuous melt pool interference provides a consistent heat input and cooling path, forming a uniform and stable thermal environment that promotes improved mechanical properties and relative density when compared to the intermittent melt pool interference mode.